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# FDA Denies Pfizer Petition on Premarin Generics
- URL: https://www.fdaweb.com/fda-denies-pfizer-petition-on-premarin-generics/
- Published: 2019-01-28T12:00:00.000Z
- Updated: 2026-09-15T00:57:56.000Z
- Author: David McFarland
- Tags: Drugs, #legacy-id-D5143232

FDA has denied an 8/2018 Pfizer petition urging FDA to tighten bioequivalence requirements for any ANDA submitter seeking approval for generic copies of its Premarin (conjugated estrogens) tablets. The [petition](https://www.regulations.gov/contentStreamer?documentId=FDA-2018-P-3325-0001&attachmentNumber=1&contentType=pdf&ref=fdaweb.com) sought to revise a 12/2014 draft guidance on methods for establishing active pharmaceutical ingredient sameness and bioequivalence for conjugated estrogens. Pfizer had earlier submitted comments on the “fundamentally flawed” guidance, but when FDA did not act on its recommendations, the company decided to submit the petition.

  
The petition asked FDA to require demonstrating sameness for conjugated estrogens using a publicly available liquid-chromatography/mass-spectrometry method that Pfizer developed. The company said the method was developed with input from FDA. “The Pfizer method permits a determination of sameness between a proposed generic product and Premarin based upon the mixture as a whole, and allows for a comparison across each of the different categories of components that make up the API,” the petition said.

In its [denial letter](https://www.regulations.gov/contentStreamer?documentId=FDA-2018-P-3325-0018&attachmentNumber=1&contentType=pdf&ref=fdaweb.com), FDA said that its proposed method for assessing API sameness is not fundamentally flawed and it has been shown to be “accurate, specific, and reproducible for 60 steroidal compounds.” The agency noted that it will continue to consider the recommendations for developing generic drug products for naturally-sourced conjugated estrogens on a case-by-case basis.